Re: RFA: enable LRA for rs6000 [patch for WRF]

[Michael Meissner <meissner at linux dot vnet dot ibm dot com>]

I tracked down the bug with the spec 2006 benchmark WRF using the LRA register
allocator.

At one point LRA has decided to use the CTR to hold a CCmode value:

(insn 11019 11018 11020 16 (set (reg:CC 66 ctr [4411])
        (reg:CC 66 ctr [4411])) module_diffusion_em.fppized.f90:4885 360 {*movcc_internal1}
     (expr_list:REG_DEAD (reg:CC 66 ctr [4411])
        (nil)))

Now movcc_internal1 has moves from r->h (which includes ctr/lr) and ctr/lr->r,
but it doesn't have a move to cover the nop move of moving the ctr to the ctr.
IMHO, LRA should not be generating NOP moves that are later deleted.

There are two ways to solve the problem.  One is not to let anything but int
modes into CTR/LR, which will also eliminate the register allocator from
spilling floating point values there (which we've seen in the past, but the
last time I tried to eliminate it I couldn't).  The following patch does this,
and also changes the assertion to call fatal_insn_not_found to make it clearer
what the error is.

I imagine, I could add a NOP move insn to movcc_internal1, but that just
strikes me as wrong.

Note, this does not fix the 32-bit failure in dealII, and I also noticed that I
can't bootstrap the compiler using --with-cpu=power7, which I will get to
tomorrow.

2013-04-16  Michael Meissner  <meissner@linux.vnet.ibm.com>

	* config/rs6000/rs6000.opt (-mconstrain-regs): New debug switch to
	control whether we only allow int modes to go in the CTR, LR,
	VRSAVE, VSCR registers.
	* config/rs6000/rs6000.c (rs6000_hard_regno_mode_ok): Likewise.
	(rs6000_debug_reg_global): If -mdebug=reg, print out if SPRs are
	constrained.
	(rs6000_option_override_internal): Set -mconstrain-regs if we are
	using the LRA register allocator.

	* lra.c (check_rtl): Use fatal_insn_not_found to report constraint
	does not match.

-- 
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460, USA
email: meissner@linux.vnet.ibm.com, phone: +1 (978) 899-4797

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